The use of photon energy beams is well known. Photon energy beams can be used for a variety of purposes, ranging for example from the transmission of signals and information to the cutting of material, such as the use of lasers to cut sheet metal. At least when used for cutting, it typically is desirable for the photon energy beam to have a radially symmetrical power distribution which is constant along the length of the beam. However, in some instances the power distribution of the photon energy beam, when it reaches its target, is not consistent and symmetrical. An asymmetric power distribution reduces the efficiency of the photon energy beam. Such a non-consistent and asymmetric power distribution is particularly troublesome when the beam is used to cut material.
The initial quality of a photon energy beam is dependant on the resonator which generates the beam. It is widely acknowledged that the gas through which a photon energy beam propagates in a photon beam delivery system can adversely affect the beam. In systems in which the length of the beam path through the gas varies, such as in laser cutters with moving optics, the beam quality frequently degrades as the beam path increases. Degradation in beam quality, between the resonator and the beam's target, is often attributed to contaminants and impurities of the gas within the photon beam delivery system in the beam path, affecting characteristics such as the beam quality K factor and the divergence.
In non-sealed beam delivery systems, it is known to provide a purge system which introduces a flow of very clean, dry purge gas, such as air or nitrogen, into an enclosure surrounding the beam, creating a positive pressure within the enclosure. Since the enclosure is not sealed, the positive pressure guarantees that gas will flow from the interior of the enclosure to the ambient environment to prevent ambient contaminants and impurities from entering the enclosure. However, such positive pressure systems are not necessarily 100% effective at keeping contaminants and impurities out. For example, photon beam delivery systems on laser cutters typically use bellows to enclose the beam. During rapid movements of the gantry carrying the nozzle and beam delivery system, ambient air carrying impurities and contaminants can be pumped into the enclosure by the expansion and contraction of the bellows despite the use of a purge system.
It has been suggested that the presence of CO.sub.2 in the beam path is the source of beam propagation degradation. Although CO.sub.2 scrubbers are available, they are more expensive than the typical air cleaners. Additionally, even if CO.sub.2 is removed from the gas introduced by a purge system, ambient impurities and contaminants may still be present within the enclosure of a non-sealed beam delivery system.
There is a need in the art for a beam delivery system which eliminates, reduces or minimizes degradation of the photon energy beam along the length of the beam path, delivering to the target a beam having substantially the same beam quality as generated by the resonator. There is a need in the art for a beam delivery system which delivers the same beam quality regardless of the length of the beam path.